This invention relates generally to continuous stream type ink jet printers and more particularly to the aperture or nozzle plates of an ink jet printhead for such printers.
Generally, in ink jet devices employing a printhead having multiple nozzles from which continuous streams of ink droplets are emitted and directed to a recording medium or a collecting gutter, there are at least one row of nozzles or orifices in an aperture plate which receives an electrically conductive recording fluid, hereinafter called ink, from a pressurized supply reservoir. For an example of a continuous stream type ink jet printer, refer to U.S. Pat. No. 4,395,716 to Crean et al, assigned to the assignee of the present invention.
The ink may be, for example, a water-based fluid and is ejected through the nozzles in a row of parallel streams or filaments. The ink is stimulated prior to or during its exiting from the nozzles so that the stream breaks up into a series of uniform droplets at a fixed distance from the nozzles. As the droplets are formed, they are selectively charged by the application of charging voltages to charging electrodes positioned adjacent the streams at the location where they break up into droplets. The droplets which are charged are deflected by an electrical field either into a gutter for ink collection and reuse, or to a specific location on a recording medium, such as paper, which may be continuously transported at a relatively high speed across the paths of the droplets.
Printing information is transferred to the droplets through charging by the charging electrodes. The charging control voltages are applied to the charging electrodes at the same frequency as that which the droplets are generated. This permits each droplet to be individually charged so that it may be positioned at a distinct location different from all other droplets or sent to the gutter. Printing information cannot be transferred to the droplets properly unless each charging electrode is activated in phase with the droplet formation at the associated ink stream. Failure to do this results in partially charged droplets which may miss the gutter or deposit the droplet at erroneous positions on the recording medium.
It is therefore apparent that ink jet printers of the continuous stream type described above cannot be operated at their maximum capability unless the streams all have the same diameter, velocity, and rheological characteristics. All streams that have the same breakoff length will generate droplets in synchronism at the same distance from their respective nozzles. Thus, stream length, diameter, or direction variation will cause defective or reduced quality printing on the recording medium.
Current practice for the fabrication of aperture plates for continuous stream type ink jet technology is based on the electroforming of nickel using photolithographic processes, such as, for example, that disclosed in U.S. Pat. No. 4,184,925 to Kenworthy. Unfortunately, aperture plates fabricated by such processes show significant corrosion when used with the ink and often after short usage times. It is imperative that aperture plates for commercial ink jet printers be corrosion free over long periods of time, preferably in excess of one year's use.
In an article entitled "Ion-Beam Implantation" by N. Basta, High Technology, February 1985, p. 58, it is reported that corrosion has been reduced in ink-spraying nozzles by using a chromium implant. However, such implants per se are insufficient to provide usable aperture plates. A need thus remains for a commercially acceptable aperture plate which is corrosion resistant over a long operating period and for a process to fabricate such a corrosion resistant aperture plate.